Outline

Objective: Do surgical drains become colonized by skin flora from outside in? Do surgical drains become colonized by bacteria of known surgical site infections?

Methods: Surgical drains were removed under sterile conditions and the part inside of the wound was separated and labelled in four pieces starting with number 1 to 4 from the skin towards the inside of the wound. The fist 3 pieces were separated every 2 centimetres, the last piece was kept as long as the remaining drain. Each piece of a drain was transported to the microbiology testing in a separate sterile container and analyzed for bacterial growth. If growth occurred, the pathogen was identified and the colony forming units were counted. Drains were pulled on the postoperative day as specified by the surgeon.

Results and conclusions: 102 drains in 57 patients were analyzed. 15 drains (14,7%) grew organisms in 11 patients (19,3%). Two patients (6 drains, 5 with growth) had a known surgical site infection and the pathogen identified on the drain was identical to the pathogen in intraoperative biopsies, one patient with Enterococcus and one with staphylococcus capitis. Nine drains (9 of 96, 9,4%) in 9 patients of 55 non-infected patients grew organisms on the drain. The majority of this growth occurred in the parts of the drains close to the skin. The pathogens of these non-infected drain colonizations were skin flora consisting of coagulase negative staphylococcus aureus (7 drains), staphylococcus hominis (1 drain), and staphylococcus aureus (1 drain). Drains represent a foreign body and skin bacteria can colonize and migrate along these into the wound. Drains do grow microorganisms of surgical site infections. Drains constitute a surface for biofilm formation. If drains are removed on day one or two after surgery they likely do not represent a risk for drain induced surgical site infection but if left in place longer, there is potential for biofilm formation through skin bacteria and/or persistence of bacteria from surgical site infections. These biofilms do constitute a risk for “outside-in” or persistent “inside” infections.